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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Surface characterization and testing II; Proceedings of the Meeting, San Diego, CA, Aug. 10, 11, 1989

Various papers on surface characterization and testing are presented. Individual topics addressed include: simple Hartmann test data interpretation, optimum configuration of the Offner null corrector, system for phase-shifting interferometry in the presence of vibration, fringe variation and visibility in speckle-shearing interferometry, functional integral representation of rough surfaces, calibration of surface heights in an interferometric optical profiler, image formation in common path differential profilometers, SEM of optical surfaces, measuring surface profiles with scanning tunneling microscopes, surface profile measurements of curved parts, high-resolution optical profiler, scanning heterodyne interferometer with immunity from microphonics, real-time crystal axis measurements of semiconductor materials, radial metrology with a panoramic annular lens, surface analysis for the characterization of defects in thin-film processes, Spacelab Optical Viewport glass assembly optical test program for the Starlab mission, scanning differential intensity and phase system for optical metrology.

Greivenkamp, John E.↗
NASA NTRS1979

Searching for nonsolar planets

The use of infrared techniques to search for nonsolar planets is examined and compared with other possible methods. Long focus astrometry, spectroscopic radial velocity measurements and spaceborne apodization all use visible light and need further refinement to be practical. Infrared offers an advantage of about 10 to the 5th over visible light as regards the ratio of power received from star and planet. Long baseline infrared interferometry from earth orbit could place an interferometric null on the star to enhance planetary radiation and a spinning interferometer would modulate planetary emission to permit synchronous detection; such an interferometer is illustrated. The limit to sensitivity would be set by thermal radiation to the detector and the infrared component of zodiacal light.

Bracewell, R. N.↗
NASA NTRS1996

Biases In A Magnitude Limited Versus A Distant Limited Planet Search

All methods utilized to conduct a search or survey inevitably have some built-in biases. These biases are often traced to some limitation of the instrument used or some inherent character of the signal being recorded. We address these limitations for various methods used or proposed for planet detection: spectroscopy, astrometry, interferometry, and photometry. For spectroscopy, the turbulence in the photosphere limits the minimum measurable dossier velocity to 3 m/s and hence the minimum planet to star mass ratio, thereby favoring massive close-in planets. Limited available observing time will necessarily introduce additional selection biases in the targets observed and telescope aperture will limit the faintest magnitude stars to be measured; For astrometry, the angular resolution of the instrument along with motions in the photometric center of the star limit the furthest distance for which giant planets can be detected to about 10 pc and favor massive outer orbit planets around low mass non-solar like stars; For imaging interferometry, the minimum angular size of the central null limits both the distance to the star and closeness of the planet to the host star to about 1 AU at 10 pc and thus to the very few solar-like stars within 10 pc. Solar and extra-solar zodiacal emission will limit the minimum size of the detectable planet. For photometry, the inherent variability of the star does not limit the minimum planet size until earth-sized or smaller planets are considered around solar-like stars. The telescope aperture limits the faintest stars that can be monitored. As with spectroscopy, there is no inherent distant limit to the method. After addressing the limiting factors of each method, an estimate is made of the number of planets of various sizes that could be found for each stellar type based on the detection probability and the number of stars that can be searched for planets.

Koch, David↗
NASA NTRS2006

The Control System for the Keck Interferometer Nuller

This viewgraph presentation reviews the control system for the interferometer nuller for the two Keck 10 meter telescopes. This reviews the control system that was implemented to enable operation of the Keck interferometer nuller. An overview of the control system is included.

nulling↗
NASA NTRS2006

Nulling at the Keck Interferometer

The nulling mode of the Keck Interferometer is being commissioned at the Mauna Kea summit. The nuller combines the two Keck telescope apertures in a split-pupil mode to both cancel the on-axis starlight and to coherently detect the residual signal. The nuller, working at 10 um, is tightly integrated with the other interferometer subsystems including the fringe and angle trackers, the delay lines and laser metrology, and the real-time control system. Since first 10 um light in August 2004, the system integration is proceeding with increasing functionality and performance, leading to demonstration of a 100:1 on-sky null in 2005. That level of performance has now been extended to observations with longer coherent integration times. An overview of the overall system is presented, with emphasis on the observing sequence, phasing system, and differences with respect to the V2 system, along with a presentation of some recent engineering data.

interferometry↗
NASA NTRS2004

Search for general relativistic effects in table-top displacement metrology

As displacement metrology accuracy improves, general relativistic effects will become noticeable. Metrology gauges developed for the Space Interferometry Mission, were used to search for locally anisotropic space-time, with a null result at the 10 to the negative 10th power level.

displacement metrology↗
NASA NTRS2004

Search for general relativistic effects in table-top displacement metrology

As displacement metrology accuracy improves, general relativistic effects will become noticeable. Metrology gauges developed for the Space Interferometry Mission were used to search for locally anisotropic space-time, with a null result at the 10 to the negative tenth power level.

displacement metrology↗
NASA NTRS1993

Spaceborne Imaging Radar-C instrument

The Spaceborne Imaging Radar-C is the next radar in the series of spaceborne radar experiments, which began with Seasat and continued with SIR-A and SIR-B. The SIR-C instrument has been designed to obtain simultaneous multifrequency and simultaneous multipolarization radar images from a low earth orbit. It is a multiparameter imaging radar that will be flown during at least two different seasons. The instrument operates in the squint alignment mode, the extended aperture mode, the scansar mode, and the interferometry mode. The instrument uses engineering techniques such as beam nulling for echo tracking, pulse repetition frequency hopping for Doppler centroid tracking, generating the frequency step chirp for radar parameter flexibility, block floating-point quantizing for data rate compression, and elevation beamwidth broadening for increasing the swath illumination.

Huneycutt, Bryan L.↗
NASA NTRS2006

Progress in testing exo-planet signal extraction on the TPF-I Planet Detection Testbed

The TPF Interferometer (TPF-I) concept is being studied at the Jet Propulsion Laboratory and the TPF-I Planet Detection Testbed has been developed to simulate the detection process for an earthlike planet orbiting a star within about 15 pc. The testbed combines four beams of infrared light simulating the operation of a dual chopped Bracewell interferometer observing a star and a faint planet. This paper describes the results obtained this year including nulling of the starlight on four input beams at contrast ratios up to 250,000 to 1, and detection of faint planet signals at contrast ratios with the star of 2 million to 1.

nulling↗
NASA NTRS2018

The Path Towards High-Contrast Imaging with the VLTI: The Hi-5 Project

The development of high-contrast capabilities has long been recognized as one of the top priorities for the VLTI (Very Large Telescope Interferometer). As of today, the VLTI routinely achieves contrasts of a few 103 in the near-infrared with PIONIER (Precision Integrated-Optics Near-infrared Imaging ExpeRiment) (H band) and GRAVITY (K band). Nulling interferometers in the northern hemisphere and non-redundant aperture masking experiments have, however, demonstrated that contrasts of at least a few 10 (sup -3) are within reach using specific beam combination and data acquisition techniques. In this paper, we explore the possibility to reach similar or higher contrasts on the VLTI. After reviewing the state-of-the-art in high-contrast infrared interferometry, we discuss key features that made the success of other high-contrast interferometric instruments (e.g., integrated optics, nulling, closure phase, and statistical data reduction) and address possible avenues to improve the contrast of the VLTI by at least one order of magnitude. In particular, we discuss the possibility to use integrated optics, proven in the near-infrared, in the thermal near-infrared (L and M bands, 3-5 microns), a sweet spot to image and characterize young extra-solar planetary systems. Finally, we address the science cases of a high-contrast VLTI imaging instrument and focus particularly on exoplanet science (young exoplanets, planet formation, and exozodiacal disks), stellar physics (fundamental parameters and multiplicity), and extragalactic astrophysics (active galactic nuclei and fundamental constants). Synergies and scientific preparation for other potential future instruments such as the Planet Formation Imager are also briefly discussed. This project is called Hi-5 for High-contrast Interferometry up to 5 microns.

PIONIER (H band)↗
NASA NTRS2004

The Antarctic Planet Interferometer

The Antarctic Planet Interferometer is an instrument concept designed to detect and characterize extrasolar planets by exploiting the unique potential of the best accessible site on earth for thermal infrared interferometry. High-precision interferometric techniques under development for extrasolar planet detection and characterization (differential phase, nulling and astrometry) all benefit substantially from the slow, low-altitude turbulence, low water vapor content, and low temperature found on the Antarctic plateau. At the best of these locations, such as the Concordia base being developed at Dome C, an interferometer with two-meter diameter class apertures has the potential to deliver unique science for a variety of topics, including extrasolar planets, active galactic nuclei, young stellar objects, and protoplanetary disks.

interferometry↗
NASA NTRS1990

Innovative operating modes and techniques for the spaceborne imaging radar-C instrument

The operation of the spaceborne imaging radar-C (SIR-C) is discussed. The SIR-C instrument has been designed to obtain simultaneous multifrequency and simultaneous multipolarization radar images from a low earth orbit. It is a multiparameter imaging radar which will be flown during at least two different seasons. The instrument has been designed to operate in innovative modes such as the squint alignment mode, the extended aperture mode, the scansar mode, and the interferometry mode. The instrument has been designed to demonstrate innovative engineering techniques such as beam nulling for echo tracking, pulse-repetition frquency hopping for Doppler centroid tracking, generating the frequency step chirp for radar parameter flexibility, block floating point quantizing for data rate compression, and elevation beamwidth broadening for increasing the swath illumination.

Huneycutt, Bryan L.↗
DOE OSTI2011

HIGH-CONTRAST STELLAR OBSERVATIONS WITHIN THE DIFFRACTION LIMIT AT THE PALOMAR HALE TELESCOPE

We report on high-accuracy high-resolution (<20 mas) stellar observations obtained with the Palomar Fiber Nuller (PFN), a near-infrared ({approx_equal}2.2 {mu}m) interferometric coronagraph installed at the Palomar Hale telescope. The PFN uses destructive interference between two elliptical (3 m Multiplication-Sign 1.5 m) sub-apertures of the primary to reach high dynamic range inside the diffraction limit of the full telescope. In order to validate the PFN's instrumental approach and its data reduction strategy, based on the newly developed 'Null Self-Calibration' (NSC) method, we observed a sample of eight well-characterized bright giants and supergiants. The quantity measured is the source astrophysical null depth, or equivalently the object's visibility at the PFN 3.2 m interferometric baseline. For the bare stars {alpha} Boo, {alpha} Her, {beta} And, and {alpha} Aur, PFN measurements are in excellent agreement with previous stellar photosphere measurements from long baseline interferometry. For the mass-losing stars {beta} Peg, {alpha} Ori, {rho} Per, and {chi} Cyg, circumstellar emission and/or asymmetries are detected. Overall, these early observations demonstrate the PFN's ability to measure astrophysical null depths below 10{sup -2} (limited by stellar diameters), with 1 {sigma} uncertainties as low as a few 10{sup -4}. Such visibility accuracy is unmatched at this spatial resolution in the near-infrared and translates into a contrast better than 10{sup -3} within the diffraction limit. With further improvements anticipated in 2011/2012, a state-of-the-art infrared science camera and a new extreme adaptive optics system, the PFN should provide a unique tool for the detection of hot debris disks and young self-luminous sub-stellar companions in the immediate vicinity of nearby stars.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2012

Method to Enhance the Operation of an Optical Inspection Instrument Using Spatial Light Modulators

For many aspheric and freeform optical components, existing interferometric solutions require a custom computer-generated hologram (CGH) to characterize the part. The overall objective of this research is to develop hardware and a procedure to produce a combined, dynamic, Hartmann/ Digital Holographic interferometry inspection system for a wide range of advanced optical components, including aspheric and freeform optics. This new instrument would have greater versatility and dynamic range than currently available measurement systems. The method uses a spatial light modulator to pre-condition wavefronts for imaging, interferometry, and data processing to improve the resolution and versatility of an optical inspection instrument. Existing interferometers and Hartmann inspection systems have either too small a dynamic range or insufficient resolution to characterize conveniently unusual optical surfaces like aspherical and freeform optics. For interferometers, a specially produced, computer-generated holographic optical element is needed to transform the wavefront to within the range of the interferometer. A new hybrid wavefront sensor employs newly available spatial light modulators (SLMs) as programmable holographic optical elements (HOEs). The HOE is programmed to enable the same instrument to inspect an optical element in stages, first by a Hartmann measurement, which has a very large dynamic range but less resolution. The first measurement provides the information required to precondition a reference wave that avails the measurement process to the more precise phase shifting interferometry. The SLM preconditions a wavefront before it is used to inspect an optical component. This adds important features to an optical inspection system, enabling not just wavefront conditioning for null testing and dynamic range extension, but also the creation of hybrid measurement procedures. This, for example, allows the combination of dynamic digital holography and Hartmann sensing procedures to cover a virtually unlimited dynamic range with high resolution. Digital holography technology brings all of the power and benefits of digital holographic interferometry to the requirement, while Hartmann-type wavefront sensors bring deflectometry technologies to the solution. The SLM can be used to generate arbitrary wavefronts in one leg of the interferometer, thereby greatly simplifying its use and extending its range. The SLM can also be used to modify the system into a dynamic Shack-Hartmann system, which is useful for optical components with large amounts of slope. By integrating these capabilities into a single instrument, the system will have tremendous flexibility to measure a variety of optical shapes accurately.

Trolinger, James↗
NASA NTRS2005

TPF Planet Detection Testbed: demonstrating deep, stable nulling and planet detection

The design of a testbed being built at the Jet Propulsion Laboratory is described. Simulatiung a dual chopped Bracewell interferometer, the testbed comprises a four beam star and planet source and nulling beam combiner. Since achieving a stable null is of great concern the testbed has many control systems designed to achieve stability of alignment and optical path difference over long periods of time. Comparisons between the testbed and the flight system are drawn and key performance parameters are discussed. The interaction between designs for phaseplate systems that achromatically invert the electric field of one of each pair of the incoming beams to achieve the null and the choice of fringe tracking schemes is also discussed.

interferometry↗